1. Field of the Invention
The present invention relates generally to powertrain hybrid electric and electric vehicles having an electric storage system (ESS).
2. Background Art
In a hybrid electric vehicle powertrain with an electric energy storage sources (ESS), electric power can flow between the powertrain and the ESS. In some cases, the power flows to the ESS for storage. In other cases, the power flows to the powertrain for consumption.
U.S. Pat. No. 5,318,142 discloses one configuration for an ESS. It describes a system having a battery and a supercapacitor connected to a bus by separate energy conversion and control devices. The separate conversion and control devices add cost and control complexity to the system. It would be desirable to eliminate one or both of these devices.
Another shortcoming of the configuration of the ESS of the '142 patent is that it fails to maximize usage of the capacitor. Maximum capacitor usage is desirable because of the performance advantages of a capacitor relative to a battery. In particular, a capacitor has better charge and discharge rates and efficiencies relative to a battery. Further, less frequent charging and discharging of a battery increases its life expectancy.